In German Published Patent Application No. 196 21 902 is discussed a method of multiple allocation of a communication line of a control unit to different signals. An apparent object of this reference is based on a system for superimposing information, a first item of information being represented by an analog signal and a second item of information being in the form of a digital signal. A superposed signal may be formed by superimposing the digital signal on the analog signal. Since the signals are transmitted at the same time, this superimposing of signals may require synchronization. For further processing at the receiving end, this superposed signal may be broken down into the basic signals, i.e., the information analog signal and the digital information signal. It is thus possible to eliminate one input line and the terminals for this line at both ends for a controller. However, this may greatly increase the expense to form the superposed signal, in particular in synchronization, and the downstream separation of the superposed signal in the controller for further processing.
Another method of eliminating terminals on microprocessors is a circuit configuration for operation of a consumer by a microprocessor that is discussed in German Published Patent Application No. 36 24 139. A reversible bidirectional terminal provided on the microprocessor itself is used to switch a consumer as well as to detect an external consumer circuit by a manual switch. Thus, a method of using a single bidirectional input instead of separate inputs and outputs on the microprocessor may be improved such that larger, high-power consumers can be operated and displayed instead of small loads, i.e., low-power consumers. When a manual switch is operated, a potential applied to the bidirectional input of the microprocessor is pulled to ground, indicating that the manual switch has been operated, because the bidirectional input usually has a high resistance due to an internal pull-up resistor. Thus, for this special case, two functions with respect to the same consumer can be implemented at one terminal of a microprocessor. However, since the terminal used is located directly on the microprocessor, a true multifunctionality with regard to different microprocessor outputs and different consumers is not possible.